perf/x86: Activate back-to-back NMI detection for arch-PEBS induced NMIs

When two or more identical PEBS events with the same sampling period are
programmed on a mix of PDIST and non-PDIST counters, multiple
back-to-back NMIs can be triggered.

The Linux PMI handler processes the first NMI and clears the
GLOBAL_STATUS MSR. If a second NMI is triggered immediately after
the first, it is recognized as a "suspicious NMI" because no bits are set
in the GLOBAL_STATUS MSR (cleared by the first NMI).

This issue does not lead to PEBS data corruption or data loss, but it
does result in an annoying warning message.

The current NMI handler supports back-to-back NMI detection, but it
requires the PMI handler to return the count of actually processed events,
which the PEBS handler does not currently do.

Thus, modify the PEBS handlers to return the count of actually processed
events, thereby activating back-to-back NMI detection and avoiding the
"suspicious NMI" warning.

Suggested-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260824082731.1013973-23-dapeng1.mi@linux.intel.com

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